Gas diffusion shower head design for large area plasma enhanced chemical vapor deposition

ABSTRACT

Embodiments of a gas distribution plate for distributing gas in a processing chamber are provided. In one embodiment, a gas distribution plate includes a diffuser plate having an upstream side and a downstream side, and a plurality of gas passages passing between the upstream and downstream sides of the diffuser plate. At least one of the gas passages has a right cylindrical shape for a portion of its length extending from the upstream side and a coaxial conical shape for the remainder length of the diffuser plate, the upstream end of the conical portion having substantially the same diameter as the right cylindrical portion and the downstream end of the conical portion having a larger diameter. The gas distribution plate is relatively easy to manufacture and provides good chamber cleaning rate, good thin film deposition uniformity and good thin film deposition rate. The gas distribution plate also has the advantage of reduced chamber cleaning residues on the diffuser surface and reduced incorporation of the cleaning residues in the thin film being deposited.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 10/823,347, filed Apr. 12, 2004, entitled “Gas Diffusion ShowerHead Design for Large Area Plasma Enhanced Chemical Vapor Deposition”(Attorney Docket No. APPM/008657/DISPLAY/AKT/RKK), which is hereinincorporated by reference in its entirety.

BACKGROUND OF THE DISCLOSURE

1. Field of the Invention

Embodiments of the invention generally relate to a gas distributionplate assembly and method for distributing gas in a processing chamber.

2. Description of the Background Art

Liquid crystal displays or flat panels are commonly used for activematrix displays such as computer and television monitors. Plasmaenhanced chemical vapor deposition (PECVD) is generally employed todeposit thin films on a substrate such as a transparent glass substrate(for flat panel) or semiconductor wafer. PECVD is generally accomplishedby introducing a precursor gas or gas mixture into a vacuum chamber thatcontains a flat panel. The precursor gas or gas mixture is typicallydirected downwardly through a distribution plate situated near the topof the chamber. The precursor gas or gas mixture in the chamber isenergized (e.g., excited) into a plasma by applying radio frequency (RF)power to the chamber from one or more RF sources coupled to the chamber.The excited gas or gas mixture reacts to form a layer of material on asurface of the flat panel that is positioned on a temperature controlledsubstrate support. Volatile by-products produced during the reaction arepumped from the chamber through an exhaust system.

Flat panels processed by PECVD techniques are typically large, oftenexceeding 370 mm×470 mm and ranging over 1 square meter in size. Largearea substrates approaching and exceeding 4 square meters are envisionedin the near future. Gas distribution plates utilized to provide uniformprocess gas flow over flat panels are relatively large in size,particularly as compared to gas distribution plates utilized for 200 mmand 300 mm semiconductor wafer processing.

Large gas distribution plates utilized for flat panel processing have anumber of fabricating issues that result in high manufacturing costs.For example, gas flow holes formed through the gas distribution plateare small in diameter relative to thickness of the gas distributionplate, for example a 0.016 inch diameter hole through a 1.2 inch thickplate, resulting in a high frequency of drill bit breakage during holeformation. Removal of broken drill bits is time consuming and may resultin the entire gas distribution plate being scrapped. Additionally, asthe number of gas flow holes formed through the gas distribution plateis proportional to the size of the flat panel, the great number of holesformed in each plate disadvantageously contributes to a high probabilityof trouble during plate fabrication. Moreover, the high number of holescoupled with the care required to minimize drill bit breakage results inlong fabrication times, thereby elevating fabrication costs.

As the cost of materials for manufacturing the gas distribution plate isgreat, it would be advantageous to develop a gas distribution plate in aconfiguration that can be efficiently and cost effectively fabricated.Moreover, as the size of the next generation gas distribution plates isincreased to accommodate processing flat panels in excess of 1.2 squaremeters, resolution of the aforementioned problems becomes increasinglyimportant. While addressing the cost implications of the design of largegas distribution plates is important, performance attributes must not beoverlooked. For example, the configuration, location and density of gasflow holes directly impact deposition performance, such as depositionrate and uniformity, and cleaning attributes, such as cleaningefficiency and residual cleaning chemical(s) in the process chamber.

Therefore, there is a need for an improved gas distribution plateassembly that reduces the manufacturing cost, and has good depositionand cleaning performance.

SUMMARY OF THE INVENTION

Embodiments of a gas distribution plate for distributing gas in aprocessing chamber are provided. In one embodiment, a gas distributionplate assembly for a plasma processing chamber comprises a diffuserplate having an upstream side and a downstream side, and a plurality ofgas passages passing between the upstream and downstream sides, whereinat least one of the gas passages has a right cylindrical shape for aportion of its length extending from the upstream side and a coaxialconical shape for the remaining length of the diffuser plate, theupstream end of the conical portion having substantially the samediameter as the right cylindrical portion and the downstream end of theconical portion having a larger diameter.

In another embodiment, a gas distribution plate assembly for a plasmaprocessing chamber comprises a diffuser plate having an upstream sideand a downstream side in the plasma process chamber that is coupled to aremote plasma source and the remote plasma source is coupled to afluorine source, and a plurality of gas passages passing between theupstream and downstream sides, wherein at least one of the gas passageshas a right cylindrical shape for a portion of its length extending fromthe upstream side and a coaxial conical shape for the remaining lengthof the diffuser plate, the upstream end of the conical portion havingsubstantially the same diameter as the right cylindrical portion and thedownstream end of the conical portion having a larger diameter.

In another embodiment, a gas distribution plate assembly for a plasmaprocessing chamber comprises a diffuser plate having an upstream sideand a downstream side, and a plurality of gas passages passing betweenthe upstream and downstream sides, wherein at least one of the gaspassages has a first right cylindrical shape for a portion of its lengthextending from the upstream side, a second coaxial right cylindricalshape with a smaller diameter connected to the first cylindrical shape,a coaxial conical shape connected to the second cylindrical shape forthe remaining length of the diffuser plate, with the upstream end of theconical portion having substantially the same diameter as the secondright cylindrical shape and the downstream end of the conical portionhaving a larger diameter.

In another embodiment, a gas distribution plate assembly for a plasmaprocessing chamber comprises a diffuser plate having an upstream sideand a downstream side in the plasma process chamber that is coupled to aremote plasma source and the remote plasma source is coupled to afluorine source, and a plurality of gas passages passing between theupstream and downstream sides, wherein at least one of the gas passageshas a first right cylindrical shape for a portion of its lengthextending from the upstream side, a second coaxial right cylindricalshape with a smaller diameter connected to the first cylindrical shape,a coaxial conical shape connected to the second cylindrical shape forthe remaining length of the diffuser plate, with the upstream end of theconical portion having substantially the same diameter as the secondright cylindrical shape and the downstream end of the conical portionhaving a larger diameter.

In another embodiment, a method of depositing a thin film on a substratecomprises placing a substrate in a process chamber with a diffuser platehaving an upstream side and a downstream side, and a plurality of gaspassages passing between the upstream and downstream sides, wherein atleast one of the gas passages has a right cylindrical shape for aportion of its length extending from the upstream side and a coaxialconical shape for the remaining length of the diffuser plate, theupstream end of the conical portion having substantially the samediameter as the right cylindrical portion and the downstream end of theconical portion having a larger diameter, and depositing a thin film onthe substrate in the process chamber.

In another embodiment, a method of depositing a thin film on a substratecomprises placing a substrate in a process chamber with a diffuser platehaving an upstream side and a downstream side, and a plurality of gaspassages passing between the upstream and downstream sides, wherein atleast one of the gas passages has a first right cylindrical shape for aportion of its length extending from the upstream side, a second coaxialright cylindrical shape with a smaller diameter connected to the firstcylindrical shape, a coaxial conical shape connected to the secondcylindrical shape for the remaining length of the diffuser plate, withthe upstream end of the conical portion having substantially the samediameter as the second right cylindrical shape and the downstream end ofthe conical portion having a larger diameter, and depositing a thin filmon the substrate in the process chamber.

In another embodiment, a method of cleaning a process chamber comprisesplacing a substrate in a process chamber, which is coupled to a remoteplasma source and the remote plasma source is coupled to a fluorinesource, with a diffuser plate having an upstream side and a downstreamside, and a plurality of gas passages passing between the upstream anddownstream sides, wherein at least one of the gas passages has a rightcylindrical shape for a portion of its length extending from theupstream side and a coaxial conical shape for the remaining length ofthe diffuser plate, the upstream end of the conical portion havingsubstantially the same diameter as the right cylindrical portion and thedownstream end of the conical portion having a larger diameter,depositing a thin film on the substrate in the process chamber,determining if the number of processed substrates having reached apre-determined cleaning limit, repeating the steps of placing asubstrate in the process chamber, depositing a thin film on thesubstrate and determining if the number of processed substrates hasreached the pre-determined cleaning limit until the number of processsubstrates has reached the pre-determined cleaning limit, if the numberof processed substrates has not reached the pre-determined cleaninglimit, and cleaning the process chamber if the number of processedsubstrates has reached the pre-determined cleaning limit.

In yet another embodiment, a method of cleaning a process chambercomprises placing a substrate in a process chamber, which is coupled toa remote plasma source and the remote plasma source is coupled to afluorine source, with a diffuser plate having an upstream side and adownstream side, and a plurality of gas passages passing between theupstream and downstream sides, wherein at least one of the gas passageshas a first right cylindrical shape for a portion of its lengthextending from the upstream side, a second coaxial right cylindricalshape with a smaller diameter connected to the first cylindrical shape,a coaxial conical shape connected to the second cylindrical shape forthe remaining length of the diffuser plate, with the upstream end of theconical portion having substantially the same diameter as the secondright cylindrical shape and the downstream end of the conical portionhaving a larger diameter, depositing a thin film on the substrate in theprocess chamber, determining if the number of processed substrates hasreached a pre-determined cleaning limit, repeating the steps of placinga substrate in the process chamber, depositing a thin film on thesubstrate and determining if the number of processed substrates hasreached the pre-determined cleaning limit until the number of processsubstrates has reached the pre-determined cleaning limit, if the numberof processed substrates has not reached the pre-determined cleaninglimit, and cleaning the process chamber if the number of processedsubstrates has reached the pre-determined cleaning limit.

BRIEF DESCRIPTION OF THE DRAWINGS

The teachings of the present invention can be readily understood byconsidering the following detailed description in conjunction with theaccompanying drawings, in which:

FIG. 1 depicts a cross-sectional schematic view of a bottom gate thinfilm transistor.

FIG. 2A is a schematic cross-sectional view of an illustrativeprocessing chamber having one embodiment of a gas distribution plateassembly of the present invention.

FIG. 2B depicts the bottom view of an embodiment of a gas diffuser plateof the current invention.

FIG. 3 depicts a cross-sectional schematic view of a gas diffuser plate.

FIG. 4A depicts a cross-sectional schematic view of an embodiment of agas diffuser plate of the current invention.

FIG. 4B depicts the top view of a section of an exemplary embodiment ofa gas diffuser plate of the current invention

FIG. 4C depicts a cross-sectional schematic view of a variation of thegas diffuser plate design of FIG. 4A.

FIG. 5 shows the diffuser surface exposed to the process volume.

FIG. 6 shows the process flow of depositing a thin film on a substratein a process chamber with a gas diffuser plate and cleaning the processchamber.

FIG. 7 shows the secondary ion mass spectrometer (SIMS) analysis of thefluorine content of SiN film of the FIG. 3 and FIG. 4A designs.

FIG. 8A depicts a cross-sectional schematic view of a variation of thegas diffuser plate design of FIG. 4A for thicker diffuser plate.

FIG. 8B depicts a cross-sectional schematic view of another variation ofthe gas diffuser plate design of FIG. 8A.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures.

DETAILED DESCRIPTION

The invention generally provides a gas distribution plate assembly forproviding gas delivery within a processing chamber. The invention isillustratively described below in reference to a plasma enhancedchemical vapor deposition system configured to process large areasubstrates, such as a plasma enhanced chemical vapor deposition (PECVD)system, available from AKT, a division of Applied Materials, Inc., SantaClara, Calif. However, it should be understood that the invention hasutility in other system configurations such as etch systems, otherchemical vapor deposition systems and any other system in whichdistributing gas within a process chamber is desired, including thosesystems configured to process round substrates.

FIG. 1 illustrates cross-sectional schematic views of a thin filmtransistor structure. A common TFT structure is the back channel etch(BCE) inverted staggered (or bottom gate) TFT structure shown in FIG. 1.The BCE process is preferred, because the gate dielectric (SiN), and theintrinsic as well as n+ doped amorphous silicon films can be depositedin the same PECVD pump-down run. The BCE process shown here involvesonly 4 patterning masks. The substrate 101 may comprise a material thatis essentially optically transparent in the visible spectrum, such as,for example, glass or clear plastic. The substrate may be of varyingshapes or dimensions. Typically, for TFT applications, the substrate isa glass substrate with a surface area greater than about 500 mm². A gateelectrode layer 102 is formed on the substrate 101. The gate electrodelayer 102 comprises an electrically conductive layer that controls themovement of charge carriers within the TFT. The gate electrode layer 102may comprise a metal such as, for example, aluminum (Al), tungsten (W),chromium (Cr), tantalum (Ta), or combinations thereof, among others. Thegate electrode layer 102 may be formed using conventional deposition,lithography and etching techniques. Between the substrate 101 and thegate electrode layer 102, there may be an optional insulating material,for example, such as silicon dioxide (SiO₂) or silicon nitride (SiN),which may also be formed using an embodiment of a PECVD system describedin this invention. The gate electrode layer 102 is then lithographicallypatterned and etched using conventional techniques to define the gateelectrode.

A gate dielectric layer 103 is formed on the gate electrode layer 102.The gate dielectric layer 103 may be silicon dioxide (SiO₂), siliconoxynitride (SiON), or silicon nitride (SiN), deposited using anembodiment of a PECVD system described in this invention. The gatedielectric layer 103 may be formed to a thickness in the range of about100 Å to about 6000 Å.

A bulk semiconductor layer 104 is formed on the gate dielectric layer103. The bulk semiconductor layer 104 may comprise polycrystallinesilicon (polysilicon) or amorphous silicon (α-Si), which could bedeposited using an embodiment of a PECVD system described in thisinvention or other conventional methods known to the art. Bulksemiconductor layer 104 may be deposited to a thickness in the range ofabout 100 Å to about 3000 Å. A doped semiconductor layer 105 is formedon top of the semiconductor layer 104. The doped semiconductor layer 105may comprise n-type (n+) or p-type (p+) doped polycrystalline(polysilicon) or amorphous silicon (α-Si), which could be depositedusing an embodiment of a PECVD system described in this invention orother conventional methods known to the art. Doped semiconductor layer105 may be deposited to a thickness within a range of about 100 Å toabout 3000 Å. An example of the doped semiconductor layer 105 is n+doped α-Si film. The bulk semiconductor layer 104 and the dopedsemiconductor layer 105 are lithographically patterned and etched usingconventional techniques to define a mesa of these two films over thegate dielectric insulator, which also serves as storage capacitordielectric. The doped semiconductor layer 105 directly contacts portionsof the bulk semiconductor layer 104, forming a semiconductor junction.

A conductive layer 106 is then deposited on the exposed surface. Theconductive layer 106 may comprise a metal such as, for example, aluminum(Al), tungsten (W), molybdenum (Mo), chromium (Cr), tantalum (Ta), andcombinations thereof, among others. The conductive layer 106 may beformed using conventional deposition techniques. Both the conductivelayer 106 and the doped semiconductor layer 105 may be lithographicallypatterned to define source and drain contacts of the TFT. Afterwards, apassivation layer 107 may be deposited. Passivation layer 107conformably coats exposed surfaces. The passivation layer 107 isgenerally an insulator and may comprise, for example, silicon dioxide(SiO₂) or silicon nitride (SiN). The passivation layer 107 may be formedusing, for example, PECVD or other conventional methods known to theart. The passivation layer 107 may be deposited to a thickness in therange of about 1000 Å to about 5000 Å. The passivation layer 107 is thenlithographically patterned and etched using conventional techniques toopen contact holes in the passivation layer.

A transparent conductor layer 108 is then deposited and patterned tomake contacts with the conductive layer 106. The transparent conductorlayer 108 comprises a material that is essentially optically transparentin the visible spectrum and is electrically conductive. Transparentconductor layer 108 may comprise, for example, indium tin oxide (ITO) orzinc oxide, among others. Patterning of the transparent conductive layer108 is accomplished by conventional lithographical and etchingtechniques.

The doped or un-doped (intrinsic) amorphous silicon (α-Si), silicondioxide (SiO2), silicon oxynitride (SiON) and silicon nitride (SiN)films used in liquid crystal displays (or flat panels) could all bedeposited using an embodiment of a plasma enhanced chemical vapordeposition (PECVD) system described in this invention.

FIG. 2A is a schematic cross-sectional view of one embodiment of aplasma enhanced chemical vapor deposition system 200, available fromAKT, a division of Applied Materials, Inc., Santa Clara, Calif. Thesystem 200 generally includes a processing chamber 202 coupled to a gassource 204. The processing chamber 202 has walls 206 and a bottom 208that partially define a process volume 212. The process volume 212 istypically accessed through a port (not shown) in the walls 206 thatfacilitate movement of a substrate 240 into and out of the processingchamber 202. The walls 206 and bottom 208 are typically fabricated froma unitary block of aluminum or other material compatible withprocessing. The walls 206 support a lid assembly 210 that contains apumping plenum 214 that couples the process volume 212 to an exhaustport (that includes various pumping components, not shown).

A temperature controlled substrate support assembly 238 is centrallydisposed within the processing chamber 202. The support assembly 238supports a substrate 240 during processing. In one embodiment, thesubstrate support assembly 238 comprises an aluminum body 224 thatencapsulates at least one embedded heater 232. The heater 232, such as aresistive element, disposed in the support assembly 238, is coupled toan optional power source 274 and controllably heats the support assembly238 and the substrate 240 positioned thereon to a predeterminedtemperature. Typically, in a CVD process, the heater 232 maintains thesubstrate 240 at a uniform temperature between about 150 to at leastabout 460 degrees Celsius, depending on the deposition processingparameters for the material being deposited.

Generally, the support assembly 238 has a lower side 226 and an upperside 234. The upper side 234 supports the substrate 240. The lower side226 has a stem 242 coupled thereto. The stem 242 couples the supportassembly 238 to a lift system (not shown) that moves the supportassembly 238 between an elevated processing position (as shown) and alowered position that facilitates substrate transfer to and from theprocessing chamber 202. The stem 242 additionally provides a conduit forelectrical and thermocouple leads between the support assembly 238 andother components of the system 200.

A bellows 246 is coupled between support assembly 238 (or the stem 242)and the bottom 208 of the processing chamber 202. The bellows 246provides a vacuum seal between the chamber volume 212 and the atmosphereoutside the processing chamber 202 while facilitating vertical movementof the support assembly 238.

The support assembly 238 generally is grounded such that RF powersupplied by a power source 222 to a gas distribution plate assembly 218positioned between the lid assembly 210 and substrate support assembly238 (or other electrode positioned within or near the lid assembly ofthe chamber) may excite gases present in the process volume 212 betweenthe support assembly 238 and the distribution plate assembly 218. The RFpower from the power source 222 is generally selected commensurate withthe size of the substrate to drive the chemical vapor depositionprocess.

The support assembly 238 additionally supports a circumscribing shadowframe 248. Generally, the shadow frame 248 prevents deposition at theedge of the substrate 240 and support assembly 238 so that the substratedoes not stick to the support assembly 238. The support assembly 238 hasa plurality of holes 228 disposed therethrough that accept a pluralityof lift pins 250. The lift pins 250 are typically comprised of ceramicor anodized aluminum. The lift pins 250 may be actuated relative to thesupport assembly 238 by an optional lift plate 254 to project from thesupport surface 230, thereby placing the substrate in a spaced-apartrelation to the support assembly 238.

The lid assembly 210 provides an upper boundary to the process volume212. The lid assembly 210 typically can be removed or opened to servicethe processing chamber 202. In one embodiment, the lid assembly 210 isfabricated from aluminum (Al). The lid assembly 210 includes a pumpingplenum 214 formed therein coupled to an external pumping system (notshown). The pumping plenum 214 is utilized to channel gases andprocessing by-products uniformly from the process volume 212 and out ofthe processing chamber 202.

The lid assembly 210 typically includes an entry port 280 through whichprocess gases provided by the gas source 204 are introduced into theprocessing chamber 202. The entry port 280 is also coupled to a cleaningsource 282. The cleaning source 282 typically provides a cleaning agent,such as disassociated fluorine, that is introduced into the processingchamber 202 to remove deposition by-products and films from processingchamber hardware, including the gas distribution plate assembly 218.

The gas distribution plate assembly 218 is coupled to an interior side220 of the lid assembly 210. The gas distribution plate assembly 218 istypically configured to substantially follow the profile of thesubstrate 240, for example, polygonal for large area flat panelsubstrates and circular for wafers. The gas distribution plate assembly218 includes a perforated area 216 through which process and other gasessupplied from the gas source 204 are delivered to the process volume212. The perforated area 216 of the gas distribution plate assembly 218is configured to provide uniform distribution of gases passing throughthe gas distribution plate assembly 218 into the processing chamber 202.Gas distribution plates that may be adapted to benefit from theinvention are described in commonly assigned U.S. patent applicationSer. No. 09/922,219, filed Aug. 8, 2001, issued as U.S. Pat. No.6,772,827, by Keller et al.; Ser. No. 10/140,324, filed May 6, 2002; andSer. No. 10/337,483, filed Jan. 7, 2003 by Blonigan et al.; U.S. Pat.No. 6,477,980, issued Nov. 12, 2002 to White et al.; and U.S. patentapplication Ser. Nos. 10/417,592, filed Apr. 16, 2003 by Choi et al.,which are hereby incorporated by reference in their entireties.

The gas distribution plate assembly 218 typically includes a diffuserplate 258 suspended from a hanger plate 260. The diffuser plate 258 andhanger plate 260 may alternatively comprise a single unitary member. Aplurality of gas passages 262 are formed through the diffuser plate 258to allow a predetermined distribution of gas passing through the gasdistribution plate assembly 218 and into the process volume 212. Thehanger plate 260 maintains the diffuser plate 258 and the interiorsurface 220 of the lid assembly 210 in a spaced-apart relation, thusdefining a plenum 264 therebetween. The plenum 264 allows gases flowingthrough the lid assembly 210 to uniformly distribute across the width ofthe diffuser plate 258 so that gas is provided uniformly above thecenter of perforated area 216 and flows with a uniform distributionthrough the gas passages 262.

The diffuser plate 258 is typically fabricated from stainless steel,aluminum (Al), anodized aluminum, nickel (Ni) or other RF conductivematerial. The diffuser plate 258 is configured with a thickness thatmaintains sufficient flatness across the aperture 266 as not toadversely affect substrate processing. In one embodiment the diffuserplate 258 has a thickness between about 1.0 inch to about 2.0 inches.The diffuser plate 258 could be circular for semiconductor wafermanufacturing or polygonal, such as rectangular, for flat panel displaymanufacturing. FIG. 2B shows an example of a diffuser plate 258 for flatpanel display application being a rectangle with width 290 of about 30inch and length 292 of about 36 inch. The sizes of the diffuser holes,the spacing of diffuser holes, and diffuser plate are not drawn to scalein FIG. 2B.

FIG. 3 is a partial sectional view of the diffuser plate 258 that isdescribed in commonly assigned U.S. patent application Ser. No.10/227,483, titled “Tunable Gas Distribution Plate Assembly”, filed onJan. 7, 2003. For example, for a 1080 in² (e.g. 30 inches×36 inches)diffuser plate, the diffuser plate 258 includes about 16,000 gaspassages 262. For larger diffuser plates used to process larger flatpanels, the number of gas passages 262 could be as high as 100,000. Thegas passages 262 are generally patterned to promote uniform depositionof material on the substrate 240 positioned below the diffuser plate258. Referring to FIG. 3, in one embodiment, the gas passage 262 iscomprised of a restrictive section 302, a flared connector 303, a centerpassage 304 and a flared opening 306. The restrictive section 302 passesfrom the first side 318 of the diffuser plate 258 and is coupled to thecenter passage 304. The center passage 304 has a larger diameter thanthe restrictive section 302. The restrictive section 302 has a diameterselected to allow adequate gas flow through the diffusion plate 258while providing enough flow resistance to ensure uniform gasdistribution radially across the perforated center portion 310. Forexample, the diameter of the restrictive section 302 could be about0.016 inch. The flared connector 303 connects the restrictive section302 to the center passage 304. The flared opening 306 is coupled to thecenter passage 304 and has a diameter that tapers radially outwards fromthe center passage 304 to the second side 320 of the diffuser plate 258.The flared openings 306 promote plasma ionization of process gasesflowing into the processing region 212. Moreover, the flared openings306 provide larger surface area for hollow cathode effect to enhanceplasma discharge.

As mentioned earlier, large gas distribution plates utilized for flatpanel processing have a number of fabricating issues that result in highmanufacturing costs. The manufacturing cost of the quad-aperturediffuser plate design in FIG. 3 is relatively high since it requiresfour drilling steps to drill restrictive section 302, flared connector303, center passage 304 and flared opening 306 to create each gaspassage 262 and the large number of gas passages 262, for example about16,000 for a 30 inches×36 inches (or 1080 inch²) diffuser plate.

FIG. 4A is a partial sectional view of the diffuser plate 258 of thecurrent invention. The diffuser plate 258 includes about 12,000 gaspassages 262 for a 30 inches×36 inches (or 1080 inch²) diffuser plate.The gas passage 262 is generally patterned to promote uniform depositionof material on the substrate 240 positioned below the diffuser plate258. Referring to FIG. 4A, in one embodiment, the gas passage 262 iscomprised of a restrictive section 402, and a conical opening 406. Therestrictive section 402 passes from the first side 418 of the diffuserplate 258 and is coupled to the conical opening 406. The restrictivesection 402 has a diameter between about 0.030 inch to about 0.070 inch,selected to allow adequate gas flow through the diffusion plate 258while providing enough flow resistance to ensure uniform gasdistribution radially across the perforated center portion 410. Theedges of the restrictive section of the diffuser holes on the first side418 of the diffuser plate 258 could be rounded. The conical opening 406is coupled to the restrictive section 402 and flares radially outwardsfrom the restrictive section 402 to the second side 420 of the diffuserplate 258. The conical opening 406 has a diameter between about 0.2 inchto about 0.4 inch on the second side 420 of the diffuser plate 258. Thesecond side 420 faces the surface of the substrate. The flaring angle416 of the conical opening 406 is between about 20 to about 35 degrees.

The spacing between flared edges of adjacent gas passages 262 should bekept as small as possible. The flared edges could be rounded. An exampleof the spacing is 0.05 inch. The maximum spacing between flared edges ofadjacent gas passages 262 is about 0.5 inch. The total restrictionprovided by the restrictive section 402 directly affects the backpressure upstream of the diffuser plate 258, and accordingly should beconfigured to prevent re-combination of disassociated fluorine utilizedduring cleaning. The ratio of the length (411) of the restrictivesection 402 to the length (412) of the conical opening 406 is betweenabout 0.8 to about 2.0. The total thickness of diffuser plate, whichequals the summation of length 411 and length 412, is between about 0.8inch to about 1.6 inch. The conical openings 406 promote plasmaionization of process gases flowing into the processing region 212. Anexample of the quad-aperture gas passage design has the restrictivesection 402 diameter at 0.042 inch, the length of the restrictivesection 402 at 0.0565 inch, the conical opening 406 diameter on thesecond side 420 of the diffuser plate 258 at 0.302 inch, the length ofthe conical opening section at 0.0635 inch, and the flaring angle 416 at220. The total thickness of the exemplary diffuser plate is 1.2 inches.

FIG. 4B shows a section of an exemplary embodiment of a hexagonal closepack gas diffuser plate 258. The holes 450 (or gas passages 262described earlier) are arranged in a pattern of face centered hexagons460. The size of diffuser holes, and the spacing of diffuser holes arenot drawn to scale in FIG. 4B. However, other patterns of gas passages262 arrangement (or holes 450), such as concentric circles, can also beused.

FIG. 4C shows an alternative design to the design shown in FIG. 4A.During the manufacturing process of machining the restrictive section402 and the conical opening 406, a flared connecting section 405 couldbe created by using a different drill to round up (or remove) the burrsleft during drilling section 402 and conical opening 406. Aside from theaddition of this connecting section 405, the rest of design attributesof FIG. 4C are the same as the design attributes of FIG. 4A.

Comparing the quad-aperture design in FIG. 3 and the funnel design inFIG. 4A, the funnel design diffuser plate is easier to manufacture thanthe quad-aperture design diffuser plate. Funnel design in FIG. 4Arequires drilling two sections which include the restrictive section 402and the conical section 406; while the quad-aperture design in FIG. 3requires drilling of 4 sections: the restrictive section 302, flaredconnector 303, center passage 304 and flared opening 306. Drilling twosections to meet the manufacturing specification is much easier thandrilling four sections to meet the manufacturing specification. Thefunnel design in FIG. 4A also has higher manufacturing yield than thequad-aperture design in FIG. 3 due to lower total number of holes. Forexample, for a 1080 in² (e.g. 30 inches×36 inches) diffuser plate, thefunnel design has about 12,000 holes, while the quad-aperture design hasabout 16,000 holes. The funnel design diffuser plate has about 30% lessholes than the quad-aperture design diffuser plate. In addition, thefunnel design in FIG. 4A has fewer particle problems than thequad-aperture design in FIG. 3 due to its relative simplicity inremoving broken drill bits from the larger restrictive section 402 (e.g.0.040 inch and 0.055 inch), compared to the smaller restrictive section302 (e.g. 0.016 inch).

In addition to higher manufacturing yield and fewer particle problems,the total surface area of the diffuser plate 258 exposed to the processvolume 212 of the funnel design is less than the quad-aperture design,which would reduce the amount of residual fluorine on the diffuser plate(or shower head) from the cleaning process. Reduced residual fluorinecould greatly reduce the fluorine incorporation in the film duringdeposition process. Incorporation of fluorine in the gate dielectric (orinsulating) film, such as SiO₂, SiON or SiN, generates defect centersthat degrade thin film transistor (TFT) device performance, such asV_(t) (threshold voltage) shift and I_(on) (drive current) reduction. Ithas been found that if the incorporated contaminants of a gatedielectric film, such as SiO₂, SiON or SiN, exceed 1E20 atom/cm³, theTFT device performance could be severely affected. Besides, thequad-aperture design also creates higher back pressure when the cleaninggas is flowing through the gas distribution plate. The disassociatedfluorine utilized to clean the plate has an increased propensity torecombine when the back pressure is higher, disadvantageouslydiminishing cleaning effectiveness.

A film deposition chamber requires periodic cleaning to reduce the filmbuild-up along chamber surfaces, which might flake off to createparticle problems in the process chamber. An example of the cleaningprocess is the remote plasma source (RPS) clean, which utilizes fluorinecontaining plasma, generated from fluorine containing gases, such asNF₃, SF₆, F₂, C₂F₆, C₃F₆ or C₄F₈O etc., to clean. After the cleaningstep, a purge gas is used to purge out residual fluorine; however, someresidual fluorine species might remain on the chamber and diffuser platesurface areas. The darkened lines (501) in FIG. 5 show the funnel designdiffuser surface exposed to the process volume 212. Table 1 compares thetotal exposed surface areas of two funnel designs (0.040 inch and 0.055inch restrictive section diameters) and a quad-aperture design. Thediameter of the flared end of both funnel designs is 0.302 inch and theflaring angle is 22°. The restrictive section 402 length for both funneldesigns is 0.565 inch, while the length of the flared opening 406 forboth designs is 0.635 inch. As for the quad-aperture design, thediameter of the restrictive section 302 is 0.016 inch, the diameter ofthe center passage 304 is 0.156 inch, the large diameter of the flaredopening 306 is 0.25 inch and the flaring angle is 22°, the length ofrestrictive section is 0.046 inch, the length of the flared connector303 is 0.032 inch, the length of the center passage 304 is 0.88 inch andthe length of the flared opening 306 is 0.242 inch. The quad-aperturedesign has highest number of diffuser holes and highest total diffusersurface area. Both 0.040 inch and 0.055 inch funnel designs haverelatively close total exposed diffuser surface areas, which are abouthalf the total exposed diffuser surface area of the quad-aperturedesign.

Number of diffusers on a 30 × 36 inch² diffuser Total exposed diffuserDiffuser Type plate surface area (inch²) Quad-aperture 16188 10594 0.055inch Funnel 11824 5352 0.040 inch Funnel 11824 5666

Table 1 compares the total exposed surface arears of two funnel designs(0.040 inch and 0.055 inch restrictive section diameters) and aquad-aperture design.

FIG. 6 shows an example of a process flow 600 of depositing a thin filmon a substrate in a process chamber with a gas diffuser plate andcleaning the process chamber when cleaning is required. The processstarts at step 601, followed by step 602 of placing a substrate in aprocess chamber with a diffuser plate. Step 603 describes depositing athin film on the substrate in the process chamber. After step 603, thesystem decides whether the number of processed substrates has reached apre-determined cleaning limit at step 604. The pre-determined cleaninglimit could be 1 substrate or more than 1 substrate at step 606. If thecleaning limit has not been reached, the process sequence goes back tostep 602 of placing another substrate in the process chamber. If thecleaning limit has reached the pre-determined cleaning limit, theprocess sequence goes to step 605 of cleaning the process chamber. Afterchamber cleaning at step 605, the system decides whether the number oftotal processed substrates has reached a pre-determined limit. If thecleaning limit has not been reached, the process sequence goes back tostep 601 of starting the deposition process. If the cleaning limit hasbeen reached the pre-determined limit, the deposition process stops atstep 607. Process flow 600 is only used as an example to demonstrate theconcept. The invention can also apply to process flows that involvesother process steps or sequences, but fit into the general concept ofdeposition and cleaning.

FIG. 7 shows the secondary ion mass spectrometer (SIMS) analysis of thefluorine content of film stacks, which contain SiN film, deposited withdiffuser plates of the two designs. The film stack analyzed includesabout 500 Å phosphorus doped (n+) amorphous silicon film, about 2200 Åamorphous silicon film, followed by about 4500 Å silicon nitride film ona glass substrate. The amorphous silicon and the silicon nitride filmshave been sequentially deposited with the same diffuser plate (or showerhead) in the same PECVD chamber. Curve 701 shows the fluorine content ofthe 0.055 inch funnel design in the SiN film (less than 1E18 atom/cm³)is more than one order of magnitude lower than the films processed withthe quad-aperture design diffuser plate (curve 702, about 5E19atom/cm³). The lower fluorine content resulting from the funnel designis possibly due to lower total surface area of the diffuser plate 258exposed to the process volume 212 compared to the quad-aperture design.

Chamber cleaning is accomplished by remote plasma source (RPS) cleanwhich uses the fluorine radicals (F*) generated from fluorine-containinggases, such as NF₃, SF₆, F₂, C₂F₆, C₃F₆ or C₄F₈O etc. Thefluorine-containing gas (or gases) could be diluted by an inert gas,such as argon (AR), to help sustain the plasma. However, the inert gasis optional. Generally, the cleaning process is performed with inert gasflowing at between about 0 slm to about 6 slm, fluorine containing gasflowing at between 1 slm to about 6 slm and the pressure of the remoteplasma source generator is maintained at between 0.5 Torr to 20 Torr.Equation (1) shows the example of using NF₃ as the cleaning gas:

NF₃→N*+3F*  (1)

The fluorine radical (F*) can also recombine to form fluorine gas (F₂),which does not have the same cleaning effect as the fluorine radical(F*) for SiN film. The reduction of cleaning efficiency due to fluorineradical recombination is stronger on SiN film cleaning than on amorphoussilicon film cleaning, since amorphous silicon can also be cleaned bythermal F₂ processing. Equation (2) shows the reaction of fluorineradical recombination.

2F*→F₂  (2)

The fluorine radicals can recombine before they reach the reactionchamber. Although not wishing to be bound by any theory, unlessexplicitly set forth in the claims, narrower passages in the diffusersand higher back pressure in plenum 264 could enhance fluorine radicalrecombination prior to entering the process volume 212 and could reducethe cleaning efficiency.

Table 2 compares the remote plasma source cleaning rates for SiN filmand α-Si film deposited in a PECVD chamber under identical conditionsfor the three designs mentioned in Tables 2 and 3. The remote plasmasource cleaning species is generated by flowing 4 slm Ar and 4 slm NF₃into an ASTeX remote plasma source (RPS) generator that is maintained at6 Torr. The ASTeX remote plasma source generator is made by MKSInstruments, Inc. of Wilmington, Mass.

Cleaning rate (Å/min) Film Quad-aperture 0.055 in. Funnel 0.040 in.Funnel SiN 7806 9067 7517 α-Si 5893 6287 5595

Table 2 compares the RPS clean rate of 3 types of diffuser design forSiN and α-Si films.

The results show that 0.055 inch funnel shaped diffuser has the bestcleaning performance, followed by the quad-aperture design and with0.040 inch funnel being the last. The result is likely due to the lowerback pressure and less restrictive diffuser path of the 0.055 inchfunnel diffuser compared to the quad-aperture and 0.040 inch funneldesign, which results in less F* recombination and higher cleaningefficiency.

Table 3 shows the back pressure (Pb) of the RPS cleaning process when Arflow is at 4 slm and NF₃ is between 0-4 slm, for both RPS plasma on andoff conditions.

Pb (mTorr), Pb (mTorr), Pb (mTorr), Flow (slm) Quad-aperture 0.055 inchFunnel 0.040 inch Funnel NF₃ Pb_(plasma-off) Pb_(plasma-on)Pb_(plasma-off) Pb_(plasma-on) Pb_(plasma-off) Pb_(plasma-on) 0 12801280 930 930 1260 1260 1 1530 1840 1070 1310 1450 1730 2 1770 2370 12001650 1640 2150 3 2000 2850 1330 1940 1810 2530 4 2220 3300 1470 22101960 2880

The 0.055 inch funnel diffuser has lowest back pressure and has least F*recombination and highest SiN film clean rate. However, the backpressure of the quad-aperture design is higher than the back pressure of0.040 inch funnel design and yet the cleaning rate of the quad-aperturedesign is higher than 0.040 inch funnel design. This shows thatrecombination due to pressure difference alone does not explain thecleaning rate result. The recombination in the diffuser also plays animportant role.

Table 4 compares the narrowest diameters, lengths and volumes of thediffuser passages of quad-aperture and 0.040 inch funnel designs. The0.040 inch funnel design has a larger passage volume compared to thequad-aperture design. The larger passage volume could allow additionalfluorine radical recombination than in the narrow diffuser passage andaffect the clean rate result.

Quad-aperture 0.040 in. Funnel Narrowest diameter in 0.016 0.040 thediffuser passage (in.) Length of narrowest 0.046 0.565 diffuser passage(in.) Volume of narrowest 0.00001 0.00071 diffuser passage (in³)

Table 4 compares the diameter, the length and the volume of thenarrowest section in the diffuser for the quad-aperture and 0.040 inchfunnel designs.

Clean rate is also dependent upon cleaning gas (such as NF₃)dissociation efficiency. Table 5 shows the chamber pressure (in theprocess volume 212) data of the three designs under RPS cleaningprocess. The chamber pressure for all three diffuser designs are all ina similar range.

Pc (mTorr), Pc (mTorr), Pc (mTorr), Flow (slm) Quad-aperture 0.055 inchFunnel 0.040 inch Funnel NF₃ Pc_(plasma-off) Pc_(plasma-on)Pc_(plasma-off) Pc_(plasma-on) Pc_(plasma-off) Pc_(plasma-on) 0 345 345330 330 323 323 1 391 460 374 451 365 430 2 438 584 420 567 409 536 3483 692 464 676 452 635 4 528 796 506 773 494 731

Table 5 compares the chamber pressure of 3 types of diffuser designunder Different NF₃ flow and when plasma is on and off.

NF₃ dissociation efficiency is directly proportional to the ratio of thenet pressure increase when plasma is on to the net pressure increasewhen plasma is off. Table 6 shows the ratio of the net pressure increasewhen plasma is on to the net pressure increase when plasma is off forthe quad-aperture, 0.055 inch funnel and 0.040 inch funnel designs.ΔPc_(plasma-on) represents the pressure difference between the chamberpressure under certain NF₃ flow to the chamber pressure under 0 NF₃ flowwhen the plasma is on. Similarly, ΔPc_(plasma-off) represents thepressure difference between the back pressure under certain NF₃ flow tothe chamber pressure under 0 NF₃ flow when the plasma is off. The ratioof ΔPc_(plasma-on) over ΔPc_(plasma-off) quantifies the NF₃ dissociationefficiency. The dissociation efficiency decreases with the increase ofNF₃ flow rate. The dissociation efficiency is highest for 0.055 inchfunnel design, followed by the quad-aperture design and then 0.040 inchfunnel design. The NF₃ dissociation efficiency data correlate with thecleaning rate data.

ΔPc_(plasma-on)/ ΔPc_(plasma-on)/ ΔPc_(plasma-on)/ NF₃ flow rateΔPc_(plasma-off), ΔPc_(plasma-off), ΔPc_(plasma-off), (slm)Quad-aperture 0.055 in. Funnel 0.040 in. Funnel 1 2.50 2.75 2.55 2 2.572.63 2.48 3 2.51 2.58 2.42 4 2.46 2.52 2.39

Table 6 compares the ratio of the net pressure increase when plasma ison to The net pressure increase when plasma is off for the 3 designs.

In addition to cleaning efficiency, the impact of the diffuser design onthe deposition performance should also be examined to ensure depositionperformance meets the requirements. Table 7 compares the SiN and α-Sideposition uniformities and rates using the different diffuser designsunder the same process conditions for the 3 diffuser designs. The SiNfilm is deposited using 600 sccm SiH₄, 2660 sccm NH₃ and 6660 sccm N₂,under 1.5 Torr and 3050 watts source power. The spacing between thediffuser plate and the support assembly is 1.09 inch. The processtemperature is maintained at about 355° C. The α-Si film is depositedusing 1170 sccm SiH₄ and 4080 sccm H₂, under 3.0 Torr and 950 wattssource power. The spacing between the diffuser plate and the supportassembly is 1.09 inch. The process temperature is maintained at 355° C.

Quad-aperture 0.055 inch Funnel 0.040 inch Funnel Dep rate UniformityDep rate Uniformity Dep rate Film Uniformity (%) (Å/min) (%) (Å/min) (%)(Å/min) SiN 3.8 1746 4.3 1738 3.2 1740 α-Si 3.9 1272 4.5 1261 4.4 1226Table 7 compares the SiN and the α-Si films deposition uniformities andrates for the 3 designs.

The results show that the deposition rates and uniformities of the threedesigns are relatively comparable. The deposition rates are about thesame for the three designs. The uniformity of 0.055 inch funnel designis worse than the quad-aperture design. However, the uniformity can beimproved by narrowing the diameter of the restrictive section 402 (0.040inch vs. 0.055 inch). The uniformity of 0.040 inch funnel design (3.2%and 4.4%) is better than 0.055 inch funnel design (4.3% and 4.5%). ForSiN film, the 0.040 inch funnel design (3.2%) is even better than thequad-aperture design (3.8%). Other film properties, such as film stress,reflective index, and wet etch rate, are equivalent for the threedesigns. The results show that the film uniformity is affected by thediffuser design and can be tuned by adjusting the diameter of therestrictive section. The results also show that the funnel design canachieve the same deposition properties, such as uniformity, depositionrate, film stress, reflective index and wet etch rate, as thequad-aperture design.

In addition to the diffuser design, process pressure can also affectdeposition rate and uniformity. Table 8 shows the effect of processpressure (or chamber pressure) on uniformity and deposition rate for0.055 inch funnel design diffuser. Lower chamber pressure gives betteruniformity and lower deposition rate.

Chamber pressure (Torr) Uniformity (%) Deposition rate (Å/min) 1.2 3.91545 1.5 5.5 1756 1.8 5.1 1784

Table 8 shows the deposition pressure, uniformity and deposition rate ofSiN film using a 0.055 inch funnel design diffuser plate.

The funnel design diffuser plate is easier to manufacture compared tothe quad-aperture design diffuser plate. Therefore, the yield and costof manufacturing the funnel design diffuser plate is improved. Inaddition to ease of manufacturing, the funnel design diffuser plate alsohas the benefit of less residual fluorine on the diffuser plate afterRPS clean. This results in less fluorine incorporation in the gatedielectric films and improved device performance. The funnel designcould have better or equivalent clean rate and efficiency compared tothe quad-aperture design, depending on the diameter of the restrictivesection 402 selected. The funnel design also could have deposition rateand uniformity performance equivalent to the quad-aperture design.

For a flat panel display with larger surface area, diffuser plate 258with larger top surface area may be required. With the increase of topsurface area, the thickness of the diffuser plate 258 may increase tomaintain the strength in supporting the diffuser plate. FIG. 8A shows avariation of the funnel design in FIG. 4A for a thicker diffuser plate.All the corresponding design attributes of FIG. 8A are same as FIG. 4A.The guidelines used to design the restrictive section 802, the flaredsection 806, and flaring angle 816 are similar to the guideline used todesign the restrictive section 402, the conical opening 406, and flaringangle 416 of FIG. 4A respectively. The presently preferred configurationof the flared section 806 is the conical cross-section shown in FIG. 8A.However, other configurations including concave cross-sections, such asparabolic, and convex cross-sections, can be used as well. Thedifference between FIG. 8A and FIG. 4A is that FIG. 8A is thicker by thelength 801. A larger diameter section 804 can be created between thefirst side 818 of the diffuser plate 258 and the restrictive section802. The large diameter section 804 is connected to the restrictivesection 802 by a flared connector 803. During the manufacturing processof machining the restrictive section 802 and the larger diameter section804, the flared connecting section 803 is created by using a differentdrill to round up (or remove) the burrs left during drilling sections802 and 804. Since the large diameter section 804 has larger diameterthan restrictive section 802, it only slightly increases themanufacturing time and does not affect manufacturing yield. The diameterof the larger diameter section 804 should be at least two times thediameter of the restrictive section 802 to ensure that the addition ofthe larger diameter section also does not change the backpressure andchamber pressure during processing as compared to the funnel design inFIG. 4A. Due to this, the deposition process and the qualities of thefilm deposited using the design in FIG. 8A are similar to the depositionprocess and the qualities of the film deposited by the funnel design ofFIG. 4A. The larger diameter section 804 has a diameter between about0.06 inch to about 0.3 inch. The edges of the larger diameter section804 of the diffuser holes on the first side 818 of the diffuser plate258 could be rounded. The ratio of the length 801 of the larger diametersection to the length 811 of the restrictive section 802 should bebetween about 0.3 to about 1.5. The total thickness of the diffuserplate, which equals the summation of length 801, length 811 and length812, is between about 1.0 inch to about 2.2 inch.

FIG. 8B shows an alternative design to the design shown in FIG. 8A.During the manufacturing process of machining the restrictive section802 and the flared section 806, a flared connecting section 805 could becreated by using a different drill to round up (or remove) the burrsleft during drilling sections 802 and 806. Aside from the addition ofthis connecting section 805, the rest of design attributes of FIG. 8Bare the same as the design attributes of FIG. 8A.

Although several preferred embodiments which incorporate the teachingsof the present invention have been shown and described in detail, thoseskilled in the art can readily devise many other varied embodiments thatstill incorporate these teachings.

1. A method of depositing a thin film on a substrate, comprising:placing a substrate in a process chamber with a diffuser plate having anupstream side, a downstream side, and a plurality of gas passagespassing between the upstream and downstream sides, wherein each of thegas passages has a first cylindrical shape for a portion of its lengthextending from the upstream side, a coaxial conical shape for a portionof its length extending from the downstream side, and a second coaxialcylindrical shape with a smaller diameter than the first cylindricalshape disposed between the first cylindrical shape and the conicalshape, wherein the downstream end of the conical shape has a largerdiameter than the upstream; flowing a gas through the plurality of gaspassages; generating plasma between the diffuser plate and thesubstrate, such that a hollow cathode effect is created within theconical shape of the gas passages; and depositing a thin film on thesubstrate in the process chamber.
 2. The method of claim 1, wherein thediffuser plate is rectangular.
 3. The method of claim 2, wherein the gascomprises a mixture of a silicon containing gas and a nitrogencontaining gas.
 4. The method of claim 2, wherein the gas comprises amixture of a silicon containing gas and a hydrogen containing gas. 5.The method of claim 2, further comprising modifying the diameter of thesecond cylindrical shape to adjust the deposition rate.
 6. A method ofdepositing a thin film on a substrate, comprising: placing a substratein a process chamber coupled to a silicon source, the process chamberhaving a diffuser plate having an upstream side, a downstream side, anda plurality of gas passages passing between the upstream and downstreamsides, wherein each of the gas passages has a first cylindrical shapefor a portion of its length extending from the upstream side, a secondcoaxial cylindrical shape with a smaller diameter for a portion of itslength extending downstream of the first cylindrical shape, and acoaxial conical shape extending downstream from the second cylindricalshape for the remaining portion of the diffuser plate length, with theupstream end of the conical portion having substantially the samediameter as the second cylindrical shape and the downstream end of theconical portion having a larger diameter; flowing a gas through each ofgas passages; generating plasma between the diffuser plate and thesubstrate, such that a hollow cathode effect is created within theconical shape of each of the gas passages; and depositing a thin film onthe substrate in the process chamber.
 7. The method of claim 6, whereinthe diffuser plate is rectangular.
 8. The method of claim 7, wherein thegas comprises a mixture of a silicon containing gas and a nitrogencontaining gas.
 9. The method of claim 7, wherein the gas comprises amixture of a silicon containing gas and a hydrogen containing gas. 10.The method of claim 7, further comprising modifying the diameter of thesecond cylindrical shape to adjust the deposition rate.
 11. A method ofcleaning a process chamber, comprising: placing a substrate in a processchamber coupled to a remote plasma source and the remote plasma sourceis coupled to a fluorine source, the process chamber having a diffuserplate with an upstream side, a downstream side, and a plurality of gaspassages passing between the upstream and downstream sides, wherein eachof the gas passages has a first cylindrical shape for a portion of itslength extending from the upstream side, a second coaxial cylindricalshape with a smaller diameter for a portion of its length extendingdownstream of the first cylindrical shape, and a coaxial conical shapeextending downstream from the second cylindrical shape for the remainingportion of the diffuser plate length, with the upstream end of theconical portion having substantially the same diameter as the secondcylindrical shape and the downstream end of the conical portion having alarger diameter; flowing a gas through each of gas passages; generatingplasma between the diffuser plate and the substrate, such that a hollowcathode effect is created within the conical shape of each of the gaspassages; depositing a thin film on the substrate in the processchamber; determining if the number of processed substrates has reached apre-determined cleaning limit; repeating the placing a substrate in theprocess chamber, flowing a gas, generating a plasma, depositing a thinfilm on the substrate, and determining if the number of processedsubstrates has reached the pre-determined cleaning limit until thenumber of process substrates has reached the pre-determined cleaninglimit; and cleaning the process chamber when the number of processedsubstrates reaches the pre-determined cleaning limit.
 12. The method ofclaim 11, wherein the diffuser plate is rectangular.
 13. The method ofclaim 12, wherein the gas comprises a mixture of a silicon containinggas and a nitrogen containing gas.
 14. The method of claim 12, whereinthe gas comprises a mixture of a silicon containing gas and a hydrogencontaining gas.
 15. The method of claim 12, wherein the cleaning isperformed by a remote plasma source cleaning process with inert gasflowing at between about 0 slm to about 6 slm, fluorine containing gasflowing at between 1 slm to about 6 slm, and the pressure of the remoteplasma source generator is maintained at between about 0.5 Torr to about20 Torr.
 16. The method of claim 15, wherein the inert gas is argon andthe fluorine containing gas is nitrogen trifluoride.
 17. The method ofclaim 16, further comprising modifying the diameter of the secondcylindrical shape to adjust the cleaning rate.
 18. The method of claim12, further comprising modifying the diameter of the second cylindricalshape to adjust the deposition rate.